Photoconductive properties of poly-n-vinyl carbazole



nited States Patent 3,485,624 PHOTOCONDUCTIVE PROPERTIES OF POLY-N-VINYLCARBAZOLE Roger P. J. G. Thiebaut, Jean-Pierre C. G. Dubosc, and

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It has also been found that much more sensitive photoconductive coatingswere obtained when crystalline poly- N-vinyl carbazole was used insteadof the amorphous polymer. By comparison with the amorphous poly-N-vinylcarbazole, the crystalline polymer shows a T period,

Claude A. L. L. Mercier, Vincennes, 'Frau'ce, assiguors to Eastman KodakCompany, Rochester, N a such as defined hereunder, which is more thantwice poration of New Jersey smaller (about 6 to 8 seconds instead of 17to 20 seconds) No Drawing. Filed June 7, 1966, Ser. N 55 and thepractical exposure time, which is also defined f- G03g 5/ 06; Cosf 7/ 16hereunder, is divided by a still greater factor (4 to 5 CL Z'Ckmns 10seconds instead of 12 to 30 seconds).

In this specification, the T period is the time required for thepotential of a photoconductive layer to ABSTRACT OF THE DISCLOSURE reachof the value of the potential after the initial According to the presentin a Substantial charge, when said layer is subjected to an illuminationof Crease in Photographic Speed Of PhOtOCOndllctiVe O 15 13,600 1x. Thepractical exposure time is the minimum ings containing poly-N-vinyl carazole is obta n d by exposure time in seconds, under the same 13,600 lx.heat treatment of such coatings at a temperature in the ill i tion,required to obtain the best possible image range from about I0 about I'a time Without any background fog, with magnetic brush deperiod fromabout 15 minutes to about 1 hour. velopment. Thus the lowest numberindicates the highest photographic speed.

The heat treatment may be conducted as well on coat- This inventionrelates to electrophotography. More ings comprising either commercialamorphous poly-N- particularly, the invention relates toelectrophotographic vinyl carbazole or on crystalline poly-N-vinylcarbazole. elements comprising a photoconductive insulating coat-Examples of commercial amorphous poly-N-vinyl carbaingonasupport. zoleare Luvican M-170 or M-710 sold by Badische PolyN-vinyl carbazole is acompound used for its Anilin Soda Fabrik. Crystalline polymers withwhich photoconductive properties in certain reproduction procweexperimented were synthesized in our laboratory by esses which utilizeelectrostatic charges. Use of poly-N- the process decsribed in BelgianPatent No. 606,790. vinyl carbazole as an organic photoconductor inelectro- With both amorphous and crystalline samples, the resultsphotographic elements is described in numerous literaobtained by heattreatment were quite similar. We prefer ture references, for example, inUS. Patent No. 3,037,861, the crystalline materials because they providebetter repatented June 5,1962. sistance to degradation by heating. Withboth types,

An object of the invention is to provide improved elechowever, at theannealing temperatures used, heat detrophotographic elements comprisingan annealed photogradation was slight enough to be tolerable. conductivecoating containing the organic photocon- The following examples areprovided to describe cerductor, poly-N-vinyl carbazole. tain preferredembodiments of the invention.

Another object of the invention is to provide a method for improving thephotographic speed of photoconductive EXAMPLE 1 electrically insulatingcotaings containing the organic A solution of poly-N-vinyl carbazole inbenzene is photoconductor, poly-N-vinyl carbazole. prepared bydissolving 6 gm. Luvican M-170 in 100 ml. According to the presentinvention, a substantial inbenzene. The solution is coated on analuminum plate crease in photographic speed of photoconductive coatingsand the solvent is evaporated at room temperature in containingpoly-N-vinyl carbazole is obtained by heat air, leaving a film ofpoly-N-vinyl carbazole coated on treatment of such coatings at atemperature in the range the metal support. The coating is electricallyinsulating from about 250 C. to about 300 C. for a time in the andphotoconductive. The coated plate is placed in an range from about 15minutes to about 1 hour. The higher electric oven in a nitrogenatmosphere and heated to the temperature, the shorter the time. Attemperatures annealing temperature; the sample is annealed fora periodlower than 250 C., the effect is negligible, whereas at in the rangefrom about 15 minutes to about 1 hour. In temperatures above 300 C. thedegradation of the Table 1 are tabulated descriptions of test resultsobtained polymer is too important for it to be used in a photowithsamples prepared as described above and annealed conductive coating. forthe times and at the temperatures shown in the table.

TABLE 1 Reduction of charge in darkness, Practical Coating Initial 3minutes exposure thickness potential (percent time Heat treatment inmicrons (volts) reduction) Tlio (seconds) None 10 800 10 1. 7 30 15111111., 250 C..- 10 1,000 33 1. 7 2 mm., 250 0.. 8 650 30 1.4 2 15min., 275 0. s 600 19 3. 7 5 60111111., 275 C 6 490 28 1.1 1. 4 15 min.,300 c. 0 800 24 1.4 1. 4

3 The test results tabulated in Table 1 were obtained by firstdark-adapting each plate for several days and then applying anelectrostatic charge by means of corona discharge. The natural chargedecay after 3 minutes was observed and recorded. The T 1 no period andthe practical 4 may be made within the scope of the invention asdescribed above and as defined in the following claims.

We claim: 1. A method for improving the photographic speed ofelectrophotographic elements comprising a support and exposure t1me Suchas defined above: were also Observed coated thereon a photoconductiveelectrically insulating and recordedlayer comprising photoconductivepoly-N-vinyl carbazole,

EXAMPLE 2 said method comprising the step of annealing said electro- Theprocedure of Example 1 was repeated, except that photographic element ata temperature in the rangefrom the coating solvent used was a 53/33/14mixture of mm In the range from mlnutes benzene, methylene chloride anddioxane, with poly-N- t0 1 vinyl carbazole prepared by the processdescribed in the 2. An lmproved electrophotographic element for useaforesaid Belgian Patent No. 606,790. In Table 2 are 1nelectrophotography comprising a support and coated tabulated testsresults obtained as in Example 1. thereon an annealed, electricallyinsulating photoconduc- TABLE 2 Reduction of charge in darkness,Practical Coating Initial 3 minutes exposure thickness potential(percent time Heat treatment in microns (volts) reduction) Ti/io(seconds) 13 1,200 12 as 4 10 1, 200 40 0.4 10 1,000 74 0.1 8 1,200 430.1, 10 550 78 0.3 10 s50 85 0.2 13 1,000 01 0.4 60 min., 330 0. 12 21005 3. 5

In the last column of Table 2, the sign indicates tive coatingcomprising photoconductive poly-N-vinyl that the practical exposure timeis too small to be carbazole, said element having been heat-annealed ata measured. temperature in the range from 250300 C. for a time Indescribing certain preferred embodiments of our inin the range fromabout 15 minutes to about 1 hour. vention, we have used coatingsconsisting essentially of poly-N-vinyl carbazole. However, our inventionextends References Cited to use of the improvements with poly-N-vinylcarbazole UNITED STATES PATENTS 1n electrophotographic photoconductivecoatings which 2 863 6 may also contain other organic polymers incombination g 2 2 Vyverberg et with poly-N-vinyl carbazole. Suchcoatings are described 19 2 H0631 et in the literature. Our inventionfurther extends to use 1/1969 Inaml at 96 1-6 of the improvements withphotoconductive coatings containing photoconductive poly-N-vinylcarbazole with added sensitizers, activators, and the like, of variouskinds known and used in the arts relating to organic photoconductivecoatings.

It will be understood that modifications and variations GEORGE F.LESMES, Primary Examiner C. E. VAN HORN, Assistant Examiner US. Cl. X.R.

